1. Field of the Invention
The present invention relates to a combined active/passive heat recovery system utilized on the interior of a building structure having windows exposed to solar radiation. More specifically, the subject invention relates to such heat recovery systems wherein system regulation is developed pursuant to the use of indirect exposure of sunlight which is controlled by a reflective surface at the window opening.
2. Prior Art
The utilization of solar energy for low temperature level heating in residences as well as commercial and industrial buildings has moved over the past several decades through a number of phases involving both active and passive systems. Early work was directed toward so-called active systems utilizing external flat plate collectors located on a sloping roof to maximize radiation. Typically these collectors consisted of one or more glass sheets through which solar radiation passed to a heat absorbing surface, with water or other fluid circulated through tubing in thermal contact with the absorbing surface, and with the sides and bottom of the collector insulated to control heat loss. In these systems heat is commonly stored in remotely located water storage tanks for use either for space heating or heating of domestic water.
Disadvantages inherent in the conventional flat plate collector system are primarily the relatively low over-all efficiency of the system and problems intrinsic in locating collectors external to a house or building, such as the cost of providing adequate structural support, weather resistance, insulation and freezing protection, as well as high temperature protection during power outages or equipment malfunction.
Numerous variations of the flat plate collector have been developed in an effort to improve the cost/benefit ratio. These include reflector boosters to increase radiation intensity on the surface of the collector and thereby increase the amount of heat recovered at a given temperature level, internal shutters or louvers to reduce overheating problems during shut-off or malfunction, various automatic drainage systems or use of antifreeze to eliminate freezing problems, along with many other design improvements.
Somewhat parallel with the development of the water circulation and storage concept for flat plate collectors, various forms of circulating hot air systems were developed, some using rock bins for storing heat to be used at night or when required. Such circulating water and air designs have been the principal method of active solar energy systems.
Passive solar energy recovery systems have more recently become significant, particularly in the design of new homes. The trend has stemmed from a combined desire to improve aesthetics and reduce costs. Passive systems recover heat within a house or building by storing energy entering through a window as solar radiation in a thermal mass (as in a Trombe wall) for re-radiation into the room during nighttime hours.
Variations in the design of passive systems are numerous and include the use of louvers, shades, between-glass moveable insulation and reflectors, in addition to fixed and moveable heat storage walls, water tanks, change of phase tanks, insulating panels and the like--all in order to control room temperature more effectively during heating and cooling, increase heat storage, reduce nighttime heat losses and cost. Passive systems tend to have the advantage of improved aesthetics and internal location of components, thus eliminating the weather resistance and insulating requirements of conventional flat plate collectors. Normally they require the use of somewhat massive walls or tanks which restrict flexibility of remodeling and result in unconventional design. In many cases, incorporating large masses into a building design imposes severe structural problems. Possibly the most serious limitations of passive systems are their restricted heat storage capability and the cost problem imposed by their limited application to mass production. Also, passive systems tend to have little temperature control flexibility. Passive designs tend to be an extension of good, energy efficient house or building design, rather than a separate apparatus as characterized by the active solar energy systems.
Various types of active-passive systems have been proposed in an effort to combine the advantages of each. Some utilize circulating liquid or air within the active component, and some propose louvers or shutters to limit daytime heat gain and reduce nighttime heat loss in an otherwise passive system. Some units recommended for greenhouse environments have utilized rotating collector plates which have heat absorption material on one side and reflective material on the other. Heat conductive tubes are disposed between these materials and in thermal contact with the heat absorptive material. These collector plates have been alternatively rotated from a total absorption orientation wherein the absorptive material is positioned against the window in direct exposure to sunlight, to a total reflective mode where the reflective side of the plate is positioned against the window. Such greenhouse systems have not been ideal, however, due to mechanical difficulties in coupling fluid lines to the movable collector plates. Furthermore, the mechanical rotating means have not been well suited for simple applications within a residence where dependable operation and an aesthetic appearance are both essential.